Medical

by Simon, Expedition Doctor

As the Doctor for the team it was my responsibility to arrange all of the medical equipment for the expedition and to make sure that I was familiar with the problems associated with humans at altitude. I’ll detail these problems below but essentially they fit into 3 categories of Acute Mountain Sickness, High Altitude Cerebral Oedema (increased fluid on the brain) and High Altitude Pulmonary Oedema (fluid on the lungs) and all are related to the low oxygen levels encountered at altitude. AMS and HACE may represent opposite ends of the same disease process but I’ll deal with them separately. My aim is to make this piece informative to those who are interested and not make you all fall asleep by using too many medical terms!

Acute Mountain Sickness (AMS)

AMS is a collection of symptoms which generally occur 6-12 hours after arriving at a specific altitude and usually resolve after 1-3 days if further ascent does not occur. The main risk factors for the development of AMS are altitude gained (especially sleeping altitude above 2500m) and rate of ascent. AMS is very common among trekkers and often affects 40-50% of trekkers to the Mount Everest (4000m+) region of Nepal. As yet there have been no identifying markers of who is likely to suffer with AMS although some people do seem to be more susceptible.

The main symptoms of AMS are headache, nausea, vomiting, decreased appetite, fatigue and sleep disturbance. To put it more simply it’s like the worst hangover ever suffered without the night out beforehand! The exact mechanism that causes AMS and HACE is unknown but it’s thought to be due to the reduced oxygen level in the blood which causes an increase in blood flow to the brain resulting in slight brain swelling (oedema). The degree of brain swelling differentiates AMS from HACE.

The two methods of preventing or minimising AMS are graded ascent of less than 300m per day (sleeping height) and a rest day every 2-3 days or 1000m gained. The other is drug prophylaxis with acetazolamide (Diamox) taken 1 day prior to ascent. This drug stimulates breathing and helps to increase oxygen blood levels. Side effects of this drug are common and therefore every effort should be made to ensure the ascent profile is graded allowing time for acclimatisation.

The treatment principles of AMS are to stop further ascent and descend if there is no improvement or the condition is worsening. Oxygen, acetazolamide, dexamethasone and a high pressure chamber (e.g. Portable Altitude Chamber – see blog from 20 April) can be used for moderate/severe symptoms but in essence the best treatment is always descend, descend, descend.

High Altitude Cerebral Oedema (HACE)

HACE is a rare but life-threatening form of altitude illness and affects approximately 1-2% of those ascending above 4500m although it has been seen in people below 2500m. Those with HACE become confused, disorientated, irrational, clumsy, unsteady on their feet and begin to hallucinate. Eventually they become lethargic and sleepy before slipping into a coma and all of this can occur within 12 hours. A good test is to ask the person to walk heel to toe for 10 steps and if they are unable to do this then they should be regarded as suffering with HACE.

Anyone suffering with the symptoms of HACE should descend immediately as this can be rapidly fatal. Oxygen, regular dexamethasone and high pressure chamber can be useful to buy time if descent is not immediately possible (e.g. night time or bad weather) but the effects are only temporary and descent should occur as soon as possible. The prevention and mechanism of HACE is the same as for AMS.

High Altitude Pulmonary Oedema (HAPE) – see blog from 20 April

HAPE is also a life threatening condition which usually occurs within 2-4 days after ascent above 2500m. It usually occurs in 1-2% of those with standard ascent rates although as many as 10% of those ascending rapidly to 4500m will develop HAPE. There is no test to predict who will develop HAPE but it is slightly more common in men than women and previous episodes make those more susceptible.

HAPE may follow AMS symptoms but often occurs alone. The first symptoms of HAPE are difficulty breathing and reduced exercise tolerance, greater than expected for the altitude. This progresses to breathlessness at rest, especially at night. There may be a dry cough with occasional blood-stained sputum but a dry cough is extremely common at altitude and in most cases is not due the HAPE. Physical findings may be subtle but include increased heart rate, increased breathing rate and crackles when listening to the chest with a stethoscope but all of these can occur in people not suffering with HAPE.

The mechanism of HAPE is due to leakage of fluid into the lungs because of raised pressure within the lung blood vessels (capillaries). The reason why this occurs is unclear and is likely to be due to many factors (e.g. cold, exercise, inflammation, genetics) which is way beyond the scope of this piece.

Early recognition of HAPE is extremely important as death commonly occurs due to incorrect diagnosis and failure to descend. Again descent is the most important factor although exertion should be minimised and the patient should be carried down in a seated or upright position as lying down worsens the symptoms. Oxygen often produces an immediate and dramatic improvement and can be life saving. A high pressure chamber may relieve symptoms and allow the patient to improve sufficiently so they are able to continue descent by walking. Several drugs have been used to treat HAPE but their role should be secondary to descent. Nifedipine reduces the blood pressure in the lungs and is the most effective drug treatment. It can also be used as a prophylaxis to prevent HAPE but those who are susceptible should probably not go high.

Summary

High altitude is an abnormal environment for most people although mountaineering and trekking are both increasingly common past-times. Other factors which cause problems are extreme cold, dangerous terrain and rock falls and these probably account for the majority of injuries and deaths in the mountain environment. That being said a planned ascent allowing time for acclimatisation and education of the participants so they are aware of the potential dangers and symptoms should result in a safe expedition or trek free from medication, altitude chambers and Doctors!

References:

The High Altitude Medicine Handbook; Pollard and Murdoch, ISBN 1-85775-849-8